Tim Sheens' rotation policy has left him nursing a selection headache as Australia march towards the business end of the World Cup.

The Kangaroos beat Ireland 50-0 in Limerick on Saturday night to confirm their inevitable topping of Group A and now move on to a last-eight meeting with the United States.

Questions abound as to what side Sheens will select for that clash, with the coach having fielded different line-ups for all three games so far.

Variation has been most notable in the playmaking positions of full-back and half-back and Sheens admits he has given himself a problem.

"We had some timing issues and I blame myself for that because I have changed the halves, had two full-backs and given the halves a couple of runs. They're as cranky as hell about that and I know they're all competitive," he said after a nine-try win against the Wolfhounds.

"But we have led our pool and I think we can play better, we will improve that. We have got here and played well as a team."

On the side which will face America, he added: "It's hard to say, I didn't get any injuries so I have to get close to picking our best 17 on the next game. It's a difficult one to say and it's real headache for me because we have so many guys playing well. We have a real couple of contentious positions."

The game was heralded as a landmark one for Irish rugby league, seeing as it was held in the heart of rugby union country at Munster's Thomond Park.

A crowd of 5,021 showed up to witness it - a record for the sport in Ireland - but not all were impressed.

One Irish reporter put it to Sheens that his side had played a game in which they did not have to try, but the coach was having none of it.

"They broke a sweat, don't you worry," he said.

"The key for us was to get no injuries so we have achieved what we did."

Sheens was unhappy that so many Irish fans opted to take in a union Test in Dublin, though, adding: "It's a shame everyone went to Dublin. It would have been nice to get a nice night with a few more people."

Aside from allowing them to plant their flag in Limerick, the evening served only for Ireland to conclude a winless campaign.

They have been nilled in two of their three games - this clash and against England - and rarely got in Australia's 20-metre zone.

Coach Mark Aston had told them to live the dream on the eve of the game, but in reality it was more of a nightmare.

"It was always going to be tough. We were playing high-quality opposition," he said.

"But I'm proud of what we served up. They had double the sets we had and the penalty count played a big part. It's hard enough playing the best in the world without not getting the bounce of the ball and the rub of the green.

"But we stuck in, had a dig and showed character."

Aston has previously voiced his frustrations about a lack of players to select from and with the chance a number of his older charges could now retire from the international game, the pool may get shallower still.

The coach is remaining upbeat, though, and insists he will continue to find a solution.

"We'd like a level playing field and we only got together three Saturdays ago," he said.

"There are 48 development officers for rugby union in this area alone. How can we get them to play rugby league? But we will be smart and do what we can.